It is generally known that cobalt may be leached from higher valent cobalt containing resource material, such as cobalt (III) oxide, using a reducing agent such as sulphur dioxide in combination with sulphuric acid, to produce cobaltous sulphate and cobaltous dithionate. This is described in the following reactions:Co2O3+SO2+H2SO4=2CoSO4+H2OCo2O3+2SO2+H2SO4=2CoS2O6+H2O
Cobalt present in rechargeable lithium ion battery cathode material is in the trivalent state and is expected to be leached with sulphur dioxide and sulphuric acid. Lithium cobalt oxide, such as LiCoO2 is a common cathode material for high energy lithium ion batteries typically used in personal electronic devices is expected to leach according to the following reactions:2LiCoO2+SO2+2H2SO4=Li2SO4+2CoSO4+2H2O2LiCoO2+3SO2+2H2SO4=Li2SO4+2CoS2O6+2H2O2LiCoO2+4SO2+2H2SO4=Li2S2O6+2CoS2O6+2H2O
Experimental work conducted on leaching lithium cobalt oxide with sulphur dioxide and sulphuric acid confirmed that up to 100% extractions of lithium and cobalt were achieved and that dithionate was detected in all leach tests conducted.
Lithium nickel manganese cobalt oxide, such as LiNi0.33Mn0.33Co0.33O2 is an emerging cathode material having both high energy and high power suitable for use in electric vehicles is expected to leach according to the following reactions:2LiNi0.33Mn0.33Co0.33O2+SO2+2H2SO4=Li2SO4+2(Ni,Co,Mn)SO4+2H2O2LiNi0.33Mn0.33Co0.33O2+3SO2+2H2SO4=Li2SO4+2(Ni,Co,Mn)CoS2O6+2H2O2LiNi0.33Mn0.33Co0.33O2+4SO2+2H2SO4=Li2S2O6+2(Ni,Co,Mn)S2O6+2H2O
(Ni,Co,Mn)SO4 and (Ni,Co,Mn)S2O6 represent a mixed metal sulphate and a mixed metal dithionate respectively.
Experimental work conducted on leaching lithium nickel manganese cobalt oxide with sulphur dioxide and sulphuric acid confirmed that up to 100% extractions of lithium, nickel, manganese and cobalt were achieved and that dithionate was detected in all leach tests conducted.
Lithium nickel cobalt aluminum oxide, such as LiNi0.8Co0.15Al0.05O2 is another emerging cathode material having both high energy and high power suitable for use in electric vehicles is expected to leach according to the following reactions:2LiNi0.8Co0.15Al0.05O2+SO2+2H2SO4=Li2SO4+2(Ni,Co,Al)SO4+2H2O2LiNi0.8Co0.15Al0.05O2+3SO2+2H2SO4=Li2SO4+2(Ni,Co,Al)CoS2O6+2H2O2LiNi0.8Co0.15Al0.05O2+4SO2+2H2SO4=Li2S2O6+2(Ni,Co,Al)S2O6+2H2O
(Ni,Co,Al)SO4 and (Ni,Co,Al)S2O6 represent a mixed metal sulphate and a mixed metal dithionate respectively.
Experimental work conducted on leaching lithium nickel manganese cobalt oxide with sulphur dioxide and sulphuric acid confirmed that up to 100% extractions of lithium, nickel, cobalt and aluminum were achieved and that dithionate was detected in all leach tests conducted.
There is no known prior art method of recovering valuable metals from spent lithium ion battery cathode materials containing cobalt that uses reductive leaching with sulphur dioxide while dealing with dithionates and recovery of water in an energy efficient manner. Although U.S. Pat. No. 8,460,631 describes the processing of manganese sulphate and manganese dithionate containing liquors, which also contain sodium sulphate and sodium dithionate, it is not obvious from that invention how sodium sulphate and sodium dithionate could be processed together with cobaltous sulphate and cobaltous dithionate in the presence or absence of lithium sulphate and lithium dithionate. Furthermore, it has been discovered that the process of dealing with dithionates and recovery of water and recirculating treated solutions back to the leach in a locked cycle manner significantly improves the recovery of lithium when present.